Ari Aster’s debut feature Hereditary is one of the scariest movies in recent memory. That’s due in large part to Aster’s meticulous direction and Toni Collette’s unrestrained lead performance. But another crucial element is Colin Stetson’s unnerving score. An avant-garde saxophonist who’s worked with everyone from Arcade Fire to Tom Waits, Stetson is also known for his innovative solo records, which caught Aster’s attention before he’d even written the film’s script.

Over the last few years, Stetson has also been moving into film composing, working in everything from Westerns to thrillers. But his score for Hereditary is particularly notable, full of droning menace and discordant bursts. A few weeks before the movie’s release, I jumped on the phone with Stetson to discuss working with Ari Aster, the art of using unconventional instruments to make what initially appear to be conventional sounds, and how he used music to make the film “feel evil.”

This interview has been edited and condensed for clarity.

How did you get involved with Hereditary?

Ari called me years ago. I can’t remember exactly when, but it definitely was something in the order of at least two, if not three, years ago. He told me he had been writing this script and had been largely influenced in the writing by several of my solo records, and that had been a muse for him in all of this. He was wondering, would I be open to doing the scoring, should he actually be able to get the picture made?

So we talked a bit about the concept behind it and his motivations, and then he sent me the script. So between just Ari’s outlook, the concepts he was dealing with, and the way he talks about his work, and the way the script reads, it’s just brilliant. Lean, very unique. I knew if it was actually going to get made, I wanted to be a part of it.

He kept me in the loop gradually as things unfolded. Then last year, I guess, we started working on it in earnest. I think I started scoring just with the script in January of last year.

He’d made a lot of strong shorts, but this was his first feature. What were your initial impressions of him as a filmmaker?

He’s passionate, and he’s clear. He knows what he wants, he knows what he likes. I don’t think he would say that he does, but he has a very musical sense to his vocabulary. Sometimes there can be a disconnect between what someone wants, and how they’re talking about what they want, how they’re able to voice what they want, specifically across disciplines. With Ari, I did not find that to be the case, ever.

One of the major things that becomes an issue, even in my limited experience with films — I think I’ve only done maybe eight or nine — is replacing temp [score], replacing what was there with something new, even if what you’re now supplying is doing the job better. A lot of the time, it will be very difficult to someone who has seen this particular scene unfold over and over, dozens if not hundreds of times as they edit. It will be very difficult for them to see it with something that aesthetically contrasts what they’ve been seeing it with for so long.

So with Ari, again, a lot of the temp they were working with was music I wrote specifically for the film in those early months before they started filming. But then some of it still was music from different orchestral pieces and whatnot. Whenever I would replace something that was temp there with something that aesthetically did not in any way resemble it, Ari was just more floored by the novelty of it. That made quite the difference. That was unique. And it was a joy to work with because it really meant I had the opportunity to make this concise, cohesive entity of the score, rather than be something that had to cater to different bits and pieces and feel as though it’s this collage you’re slowly assembling.

Were there particular things he talked about wanting for the score?

He kept it very simple. There was one thing that he wanted to express: he wanted it to “feel evil.” So that was quite simple.

Beyond that, I was to avoid any semblance of sentimentality or nostalgia, and look at this as though the score itself was a character in the film. Namely, the character of the unfolding narrative. It was like establishing this additional character in the narrative, rather than having the score playing themes for each character and things like that. This was an additional character who had relationships with all of them, and how to work those, how to conceptualize that, and then play with it.

It was a challenge, and it was really fun for me to look at the scoring of something very different, and to go at it in that direction. Melodically, aesthetically, I was really trying to avoid the score attracting any undue attention to itself. I felt if the overarching feel of the score was something people were consciously aware of, then it missed the mark. It had to be tied in seamlessly to everything that was happening narratively, and everything that’s happening on-screen, so that it really only upheld the action rather than upstaging it.

In some films, obviously there are a lot of things you are fixing as a composer, be it lazy writing or a script that’s not quite there, performances that just aren’t cutting it, or a bloated edit or whatever, something not moving quick enough. But there were no things to fix in this. Ari did a fantastic job. The actors just absolutely killed it.

For me, it was an enormous project. I’ll preface this by saying that I think it was 85 minutes of music, ultimately. It was a bear, and I was working 16-hour days for a good long stretch. Other than the amount of work, it was quite a pleasure because every scene was put together just wonderfully. Every scene was acted perfectly. When you get that kind of inspiration to work with, it makes the job seem effortless.

The orchestration of the score seems unique. What instruments did you use?

The idea of hiding in plain sight was operative for me in establishing what it would be like, these multiple levels of the score. One of them, from the get-go, I wanted to avoid certain ubiquitous tropes that found throughout the genre and throughout film scoring in general. So avoiding the conventional use of strings, avoiding synths, avoiding creepy percussion — all the things I feel like a listener can maybe tune out. They get the job done, but in a way that people have heard so many times, it becomes less effective. So, how to get the same jobs done but with different sound sources that are more obscure aesthetic choices?

When you listen to the score, something that sounds like strings most likely is not. It’s probably clarinets or my voice. Something that sounds like synths is probably a contrabass clarinet or some number of them. Something that sounds like a swarm of bats, that probably is strings. Using sound sources to accomplish different ends was the first goal.

Then, in the construction of the whole thing, melodically and aesthetically, as things develop, someone who has seen the whole thing will notice that, by the end, the different sonic imagery and themes have all revealed themselves. Hopefully, in a mirror of the way that the story reveals itself. All of these things that have been aspects of the musical character get flipped on their head and take on new meaning and new emphasis as things develop.

I find I’m avoiding speaking in any specifics. I hate the idea of somebody reading this and it blowing the arc [of the film]. There were a few different levels to how I imagined doing that and avoiding certain things and focusing on others, getting results out of different instrumentation through unconventional methods of playing them or through processing and deconstruction. In terms of just the raw, “what’s there,” pound for pound, it’s probably more vocals than anything, but you’d never know it to hear it.

That’s bonkers.

Yeah, most of that comes from my voice. There is quite a bit of contrabass clarinet and bass clarinet and B-flat clarinet, for that matter. Clarinet was a huge player. There was a fair bit of my trusty alto bass saxophone strewn throughout. But, primarily, vocal basis and clarinets. A fair amount of brass, as well. All the percussive sounds from the thing come from mic’d keys on the woodwind instruments. I played everything on it and utilized everything I know how to. And then some things, I took up for the purpose of the film.

Do you prefer to work alone when scoring?

Yeah. It’s not that I don’t like to work with other people, but I generally work alone on most things, and I find it to be much simpler because my hours can be whatever they need to be, and I don’t have to rely on anybody else for any of that. So if I find that aesthetically, I’m not getting what I want, I either have to learn how to play a new instrument or how to play an instrument I already know how to play, in a different way. It keeps me moving.

How does working on a score compare to collaborating with a band or even a solo record?

Oh, I really enjoy it, extremely so. Conceptually, it is like working with a songwriter, in that in both instances, you’re working with someone whose vision you’re servicing. You’ve got to figure out what their intentions are, how best to serve that.

When I do a song for someone, I try to be as economical as possible and to think, “Okay. What does this need? What do I have in my arsenal, potentially, that can accomplish this, and how do I accomplish it in the most direct way possible?” The same thing goes for scoring. I think the prime directive should be, “Just don’t get ego in the way. Don’t inject it with anything, to try to put your print on it. Just find ways of giving the film exactly what it needs, no more and no less.” For something like this, if it’s not a breeze, it’s at least a pleasant ardor. A very satisfying process.